This invention concerns stays for windows and relates to stays of the kind comprising one or more arms or links and/or mounting plates that are connected together by one or more friction pivot joints which permit restrained pivotal movement of the stay parts, the stay being adapted and arranged for mounting on a sash and securing to the associated frame so that the sash is supported for frictionally restrained pivotal movement on and relative to the frame.
The stays of the kind aforementioned are conventionally used in pairs, one either side of the sash and associated frame. The sash may be hung on the stays for top, bottom or side opening, and the frictional restraint is provided by the design and manufacture of the pivot joints. For instance, a known form of pivot joint comprises a rivet which is clinched to exert a pressure within the joint to generate the frictional restraint.
In use of the stays of this kind, the arms or links are arranged to fold over one another and these lie in superposed relationship within the rebate of the frame when the sash is closed. In order to ensure that the sash closes to and fits within the rebate in a substantially weather proof manner, it is important that the stays be designed to bring the sash properly to the closed position, and to hold the sash in the closed position irrespective of additional fasteners that might be provided. One way of achieving this that has been employed previously is to design the stay so that one or more of the arms or links is stressed when the stay is folded and such stress is translated into forces acting on the stay to bias the sash in a direction towards the frame. This bias is referred to as "pull-in".
The amount of stress applied to the arms or links for adequate pull-in is designed by close control of distances between pivot centres and the lengths of the arms or links so that in the stressed condition at least one arm or link is induced in the closing position to bow or to flex. The flexure of the arm or link effectively produces a force acting on the sash to produce the desired pull-in.
In manufacture of such stays the precise control of the distances is difficult to maintain having regard to the different characteristics of the material used for the arms and/or links and the nature of the riveted pivot joint wherein slight variations in rivet sizes, clearance holes and clinching pressures and alignment can arise. Furthermore, it will be appreciated that the amount of flexing intended to be imparted to the arm or link is itself restricted by: the material used for the arm or link, this usually being aluminium; the clearances provided within the rebate in which the bowed arm or link is confined when the sash is closing or closed; and lastly, the strength of the pivot joint including the rivet which is highly stressed to maintain the frictional restraint in service.